1. Field of the Invention
This invention relates to a pressure control device for controlling the pressure of hydraulic fluid in the control system of an automatic transmission for a motor vehicle. More particularly, the invention pertains to a solenoid-operated pressure control valve.
2. Description of the Prior Art
SAE Technical Paper 960430 describes a hydraulic control valve for use with a solenoid, the valve having two control lands of equal diameter and a long feedback orifice that passes through a control land and a major portion of the spool shank length. That valve is moderately stable due to viscous damping through the feedback orifice. However, it exhibits slow low-temperature response. Furthermore it is difficult and expensive to manufacture, particularly because of the long feedback passage.
U.S. Pat. No. 4,678,893 describe a hydraulic control valve for use with a solenoid, the valve having three control lands of equal diameter and long orifices extending through the valve body. The valve is stable due to the presence of positive hydrodynamic damping; however, it is expensive to manufacture and require a large lateral package space.
U.S. Pat. No. 5,615,860 describes a hydraulic control valve for use with a solenoid, the valve having two control lands. Damping occurs in the electrical solenoid. The valve is simple and compact, but it is unstable because damping is not reliable. Also it is possible that hydraulic fluid may not be continuously available for hydraulic damping.
It is an object of this invention to provide an improved variable force solenoid-operated valve. The valve is stable and provides inertia damping, either through a short feedback orifice that passes through a land, or through a short damping orifice located at the pressure end. In either case, the valve is easy to manufacture, compact, and stable. It has good response time at low temperature.
The valve provides the ability to operate with these advantages at a low magnitude of load spring force and low electromagnetic force. The output pressure produced by the valve has been demonstrated to be predictable and stable over time and over a large range of line pressure.
In realizing these objects and advantages a solenoid-operated valve assembly for an automatic transmission of a motor vehicle includes a valve body having a control chamber, first, second and third ports spaced mutually along, and communicating with the control chamber; a valve spool located within the control chamber including a shank, a first land adapted to open and close the first port; a feedback orifice connecting a feedback chamber and the second port, and a second land located at an opposite end of the shank and adapted to open and close the third port; a spring urging the valve spool to move along the control chamber; and a solenoid assembly having an armature axially displaceable in response to an electric signal supplied to a coil, the armature urging the valve spool to move along the control chamber.